Due to its technical design, the rear window of a passenger car is not bordered by parallel edges. The width of the rear window glass or rear window decreases as it progresses upwardly toward the lower roof edge.
Guide rails integrated into the C-column of the car body recently have been utilized when the rear window is to be provided with a window shade. The spacing between these guide rails changes in accordance with the progression of the C-column. Consequently, it must be possible to telescopically adjust the length of a rear window shade pull rod or extension profile that is guided in the guide rails.
The extension profile of such a window shade, for example, according to DE 2004 020 531 B3 or DE 157 760 A1, is composed of a center section and two end sections. The end sections which are provided with sliding elements that slide in the guide rails, can be telescopically displaced relative to the center section.
One edge of the shade is fixed on the center section of the extension profile and the other edge is anchored on a winding shaft. The winding shaft is rigid and firmly supported in the region of the rear window shelf, or under the shelf within the car body, such that it can rotate.
In the retracted state, the end sections are completely extended out from the center section. The end sections slide into the center section when the window shade is extended up and the extension profile approaches the lower roof edge. The greatest relative movement between an end section and the center section occurs where the frictional force between the two components is the lowest. As a result, the center section may become shifted relative to the structural center of the window shade in the completely extended state such that unsightly transverse creases are formed in the shade. This can be prevented, according to the aforementioned publications, in that both end sections are coupled by means of a differential gear such that the center section inevitably remains centered between the end sections at all times. Such arrangement is effective, but relatively complicated.